Automatic control systems for starting-up turbines



Dec. 13, 1966 H. o. WALKER 3,291,147

AUTOMATIQA CONTROL SYSTEMS FOR STARTING-UP TURBINES Filed Feb; 26, 1953 Inventor By M Attorney United States Patent O M 3,291,147 AUTOMATIC CONTROL SYSTEMS FOR STARTING-U1 TURBINES Herbert Oswald Walker, West Hartlepool, England, assignor to Richardsons, Westgarth & Co. Limited, Wallsend, England FiledFeb. 26, 1963, Ser. No. 261,143 Claims priority, application Great Britain, Feb. 28, 1962, 7,884/ 62 4 Claims. (Cl. 137-17) This invention relates to automatic control systems for controlling the operation of rotary machines such as steam turbines. The invention is particularly applicable to the control of these machines during their starting-up period.

The starting-up of large steam turbines is frequently controlled through a control system which regulates the operation of the turbine up to the point where the normal running control gear takes over. In some systems this regulation is achieved by using a device which compares the actual speed of the turbine at `any instant with the intended speed set by speed-programme apparatus. If for any reason the actual turbine speed departs by more than a limited amount from the value laid down by the programme, some kind of override control can come into action so that the turbine is shut down for correction of the fault which caused the actual speed to depart from its intended value.

An improvement on this form of control system is described in United States Patent No. 3,226,558 issued December 28, 1965, which relates to a control system of such construction that, where the departure of the turbine speed from its intended Value is due to a temporary factor which does not warrant shutting down the turbine, the turbine is kept running and the speed-programme apparatus is adjusted to a new programme which ensures that the turbine will not race `when the said factor is corrected or removed. Thus, in this form of control system, departures in the speed of the machine from the intended speed are detected by speed-sensitive means which cooperate with an adjusting device for adjusting the speedprogramme apparatus so that, on the removal or correction of the factor which caused the `actual speed to depart from its intended value, the speed programme recommences at an adjusted intended speed which is not different to a harmful extent from the actual speed of the machine at that instant.

The present invention is similar to that described in the patent application referred to above, but has the .important diiference that, whereas the earlier invention `de-` pends on speed-sensitive means and speed-programme means, the control system of the present invention has acceleration-sensitive means and acceleration-programme means. By this means a more simple system is obtained.

Broadly, the control system in accordance with this invention comprises an acceleration-sensitive instrument for measuring the actual acceleration of the machine, acceleration-programme apparatus for determining the intended acceleration, and a comparator arrangement connected to the acceleration-sensitive instrument, the acceleration-programme apparatus and the controls of the machine so that, in operation, the comparator arrangement compares the two accelerations and, where necessary, alters the controls of the machine so as to maintain its actual acceleration at the intended value.

In order that the invention may be thoroughly understood an example of an automatic -control system in accordance with it will now be described with reference to the accompanying drawings, in which:

FIGURES 1 and 2 are graphs illustrating the actual and intended speed and acceleration of a turbine during its starting-up period; and

3,291,147 Patented Dec. 13, 1966 ICC which is supplied with steam through a valve 12. The' system comprises an acceleration-sensitive instrument 14 constructed to measure the actual acceleration of the turbine shaft and produce an electrical signal F1 which is dependent on the acceleration thus measured. This is achieved by using a speed-sensitive device 16 which measures the speed of the turbine shaft and feeds a signal dependent on that speed into a differentiator 18 which converts it into the acceleration signal F1. The signal is then supplied to a servo 20 where it is compared with an electrical signal F2 representing the desired or intended acceleration. Depending on the ratio of the two signals, the servo 20 ladjusts the position of the valve 12 through a servo motor 22 so as to maintain the actual acceleration of the turbine at the intended value.

The graph shown in FIGURE 1 illustrates normal operation of the turbine. Thus, the line AB represents the intended acceleration, and, provided nothing happens (such as a shortage of steam) to force the turbine to lag, it will speed up as shown by the line CD. At the point D the speed will reach the normal running value, and the running control gear will then take over.

The line VAB in FIGURE 2 again represents the intended acceleration. Suppose now, however, that at some point E on the speed curve CD a shortage of steam arises which causes the speed to lag and fall off as shown by the line EFG. The actual acceleration will now follow the dotted line HIJKL, -and when the steam supply is restored at G the turbine speed will lag very much behind the speed N which would have been attained under the conditions shown in FIGURE 1. However, there will be no sudden surge in speed since the acceleration will still be restricted to the value specified along the line MB.

The main advantage of the control system described above over that described in our earlier co-pending patent application is that the acceleration-programme apparatus 24 which produces the signal F2 does not have to be adjusted when the speed of the turbine lags behind the intended value. The system of the present invention is therefore more simple in construction and operation.

Although the invention has been described with particular reference to steam turbines, it is applicable to the control of other rotary machines such as gas turbines, electric motors and alternators.

I claim:

1. An automatic control system for controlling the operation of a steam turbine or the like comprising a speed sensitive device for measuring the speed of the turbine shaft, said speed sensitive device being capable of producing a first electrical signal representative of said speed, a differentiator which receives said rst signal and produces a second signal representative of the acceleration of said turbine shaft, means for producing a third signal representative of the desired acceleration, means for comparing said second and third signals and for controlling said turbine in response to a predetermined difference between said second and third signals.

2. An automatic control system for controlling an automatic machine such as -a steam turbine, comprising an acceleration sensitive instrument coupled to the machine and providing a first variable electrical signal representing the actual instantaneous acceleration of the machine, acceleration program apparatus providing ya second electrical signal representative of -desired acceleration -as a function of time, a comparator amplifier with input means receiving said first and second signals and delivering on its output a third signal representing their difference, and

servo motor means having its output coupled in controlling relationship t0 the machine and receiving said third signal as an input driving signal.

3. A control system according to claim 1 in which the acceleration-sensitive instrument comprises a speed-sensitive device arranged to measure the speed of the machine and feed an electrical signal dependent on that speed into a dilferentiator which converts it into `an acceleration signal.

4. A control system according to claim 1 for controlling the operation of a steam turbine, in which a servo motor is arranged to alter the setting of -a steam valve which regulates the ow of steam into the turbine.

References Cited by the Examiner UNITED STATES PATENTS Meyer 137-50 X Pearce 137-27 Morris 137-36 Carey 137-36 Eggenberger 137-27 X Quenneville 137-48 X 10 WILLIAM F. ODEA, Primary Examiner.

CLARENCE R. GORDON, Examiner. 

1. AN AUTOMATIC CONTROL SYSTEM FOR CONTROLLING THE OPERATION OF A STEAM TURBINE OR THE LIKE COMPRISING A SPEED SENSITIVE DEVICE FOR MEASURING THE SPEED OF THE TURBINE SHAFT, SAID SPEED SENSITIVE DEVICE BEING CAPABLE OF PRODUCING A FIRST ELECTRICAL SIGNAL REPRESENTATIVE OF SAID SPEED, A DIFFERENTIATOR WHICH RECEIVES SAID FIRST SIGNAL AND PRODUCES A SECOND SIGNAL REPRESENTATIVE OF THE ACCELERATION OF SAID TURBINE SHAFT, MEANS FOR PRODUCING A THIRD SIGNAL REPRESENTATIVE OF THE DEISRED ACCELERATION, MEANS FOR COMPARING SAID SECOND AND THIRD SIGNALS AND FOR CONTROLLING SAID TURBINE IN RESPONSE TO A PREDETERMINED DIFFERENCE BETWEEN SAID SECOND AND THIRD SIGNALS. 